Change in the Brightness of the bulb in cases (i), (ii) & (iii) Justification
(i) Increases
${\mathit{X}}_{\mathit{L}}=\mathit{\omega }\mathrm{L}$ As number of turns decreases, $\mathrm{L}$ decreases, hence current through bulb increases. / Voltage across bulb increases.
(ii) Decreases
Iron rod increases the inductance which increases ${\mathrm{X}}_{\mathrm{L}}$ , hence current through the bulb decreases./ Voltage across bulb decreases.
(iii) Increases
Under this condition $\left({\mathit{X}}_{\mathit{C}}={\mathit{X}}_{\mathit{L}}\right)$ the current through the bulb will become maximum / increase.